Printer having circuit for providing improved printing quality

ABSTRACT

Bit data of a received video signal is partially converted into a first signal representing a data sequence corresponding to the resolution of an LED head. The first signal is transmitted to the LED head in the form of a real printing data signal that is to be printed on a basic raster line in synchronism with a line timing signal. The remaining bit data of the received video signal, which are not converted into the first signal, are converted into a second signal representing another data sequence, and then stored in a line buffer. The second signal stored in the line buffer is transmitted to the LED head in the form of a real printing data signal that is to be printed on an additional raster line in synchronism with an additional line timing signal. The LED head drive energy with which the basic raster lines are printed and another LED head drive energy with which the additional raster lines are printed are set independently of each other. The LED head may be provided with such a resolution function.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/456,119,filed on May 31, 1995 (now U.S. Pat. No. 5,818,488, issued on Oct. 6,1998. That application (Ser. No. 08/456,119) was a division of anearlier application, Ser. No. 07/907,643, filed Jul. 2, 1992 (now U.S.Pat. No. 5,648,810, issued on Jul. 15, 1997). The present applicationclaims the benefit under 35 U.S.C. 120 of both of these priorapplications.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a non-impact printer and moreparticularly to a printer improved in printing quality to providenatural printing for a curve, a slash or the like.

2. Description of the Prior Art

Hitherto, in a non-impact printer such as an electrophotographicprinter, an electrically charged photoconductor drum is illuminated witha light source to form an electrostatic latent image on a surfacethereof, and developing is performed upon adhesion of a toner to theelectrostatic latent image to form a toner image. Then, the thusobtained toner image is transferred to a recording material to be fixedthereon.

FIG. 2 is a block diagram of a printer control circuit in a conventionalnon-impact printer. In FIG. 2, a printing control unit 1 transmits, atthe time a sheet arrives at a printing ready point, a timing signal 12,including a line and a raster timing signal, to a host or anothercontroller, and receives a video signal 11 which has been edited on eachpage in the other controller. The video signal 11 received by theprinting control unit 1 is transmitted to an LED (Light Emitting Diode)head 19 in the form of a real printing data signal 18.

FIG. 4 is a block diagram of the LED head in the conventional non-impactprinter. In FIG. 4, the LED head 19 comprises a shift register 19 a forstoring in order a line of real printing data signal 18 from theprinting control unit 1 shown in FIG. 2 in synchronism with a clocksignal 18 a, a latch 19 b for temporarily holding a line of realprinting data signal 18 stored in the shift register 19 a in accordancewith a latch signal 17, an LED group 19 c wherein LED elements, thenumber of which corresponds to that of a line of dots, are arranged, anda driver group 19 d for supplying the real printing data signal 18 heldin the latch 19 b to the LED group 19 c.

The shift register 19 a in the LED head 19 stores in order the realprinting data signal 18 in synchronism with the clock signal 18 a. Uponreceipt of a line of video signal 11, the printing control unit 1transmits a latch signal 17 to the LED head 19. The latch 19 b holds aline of real printing data signal 18 stored in the shift register 19 ain accordance with the latch signal 17. Before receiving the subsequentvideo signal 11 by the printing control unit 1, the thus held realprinting data signal 18 is transmitted to the LED group 19 c inaccordance with a printing drive signal 13, so that the correspondingLED elements are lightened.

Transmission and receipt operation of the video signal 11 is performedin the unit of print lines. FIG. 3 is an operational time chart of theconventional non-impact printer mentioned above. However, according tothe conventional non-impact printer mentioned above, the same size ofdots are printed on a sheet depending on the resolution of the LED head19 which is determined by the arrangement of the LED elements at regularintervals in a raster direction. Thus, there will be retained a serratededge-like image on a slash portion of the printed image due to theresolution.

FIGS. 5A, 5B and 5C, and FIGS. 6A, 6B and 6C are views showing printingstates according to the conventional non-impact printer. FIGS. 5A and 6Ashow 300 dots per inch (DPI) data; FIGS. 5B and 6B each show therelation between the print timing and driving energy for the LED head;and FIGS. 5C and 6C each show a real printing image.

As shown in the figures, both of the real printing images haveundesirable serrated edge-like images, since the printing is performedon the predetermined raster lines. In view of the foregoing, if onecontemplates increasing the density of the dots in order to improve theprinting quality, then it is necessary to use an LED head 19 in whichthe LED elements are arranged at closer intervals or pitches. However,such an LED head 19 encounters a lower yield in manufacture of the partswhere the LED elements are arranged, and thus becomes very expensive.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention, in view of theforegoing problems, to provide an improved printer.

It is another object of the present invention to provide a non-impactprinter capable of receiving a video signal from another controller or ahost controller, even if the video signal has a resolution higher thanthe print resolution of the printing unit, which will be defined by thearrangement pitch of the LED elements in a raster direction in the LEDhead.

It is still another object of the present invention to provide anon-impact printer capable of reducing a serrated edge-like image on aslash portion of the printed image by means of providing in appearance ahigher dot density than the arrangement pitch or interval of the LEDelements, thereby improving the printing quality.

It is still another object of the present invention to provide anon-impact printer which is inexpensive to manufacture.

In accordance with a preferred embodiment of the present invention,there is disclosed a non-impact printer provided with an LED head forprinting and control means for providing a sequence control for theprinter in its entirety in response to a control signal and a videosignal from another controller, said control means including a printdata receiving circuit adapted to receive the video signal from theother controller and transmit a timing signal to the other controller,said print data receiving circuit comprising: means for generating linetiming signals defining printing on basic raster lines; means forgenerating additional line timing signals each defining printing on anadditional raster line during an interval of a receiving timing of theline timing signals; first conversion means for converting partially bitdata of the received video signal into a first signal representative ofa data sequence corresponding to a resolution of the LED head; means fortransmitting the first signal to the LED head in the form of a realprinting data signal to be printed on the basic raster line insynchronism with the line timing signal; second conversion means forconverting the remaining bit data of the received video signal, whichare not converted into the first signal, into a second signalrepresentative of another data sequence; a line buffer for storing thesecond signal transmitted from said second conversion means; and meansfor transmitting the second signal stored in said line buffer to the LEDhead in the form of a real printing data signal to be printed on theadditional raster line in synchronism with the additional line timingsignal, wherein said control means further includes means for setting afirst LED head drive energy with which the basic raster lines areprinted and a second LED head drive energy with which the additionalraster lines are printed independently of each other.

In accordance with another preferred embodiment of the presentinvention, there is disclosed a non-impact printer provided with an LEDhead for printing and control means for providing a sequence control forthe printer in its entirety in response to a control signal and a videosignal from another controller, said control means including a printdata receiving circuit adapted to receive the video signal from theother controller and transmit a timing signal to the other controller,said print data receiving circuit comprising: means for generating linetiming signals defining printing on basic raster lines; means forgenerating additional line timing signals each defining printing on anadditional raster line during an interval of a receiving timing of theline timing signals; a line buffer for storing the received videosignal; first conversion means for reading out the video signal storedin said line buffer, converting bit data of the read out video signalinto a first signal representative of a data sequence corresponding to aresolution of the LED head, so that a resolution in a raster directionis converted into that in a sheet transfer direction; means fortransmitting the first signal to the LED head in the form of a realprinting data signal to be printed on the basic raster line insynchronism with the line timing signal; second conversion means forperforming a logical operation based on the current video signal enteredand the previous video signal on the preceding line stored in the linebuffer to generate a second signal representative of another datasequence, so that the resolution in the raster direction is convertedinto that in the sheet transfer direction; means for transmitting thesecond signal generated from said second conversion means to the LEDhead in the form of a real printing data signal to be printed on theadditional raster line in synchronism with the additional line timingsignal, wherein said control means further includes means for setting afirst LED head drive energy with which the basic raster lines areprinted and a second LED head drive energy with which the additionalraster lines are printed independently of each other.

In accordance with a further preferred embodiment of the presentinvention, there is disclosed a non-impact printer provided with an LEDhead for printing and control means for providing a sequence control forthe printer in its entirety in response to a control signal and a videosignal from another controller, said control means including a printdata receiving circuit adapted to receive the video signal from theother controller and transmit a timing signal to the other controller,said print data receiving circuit comprising: means for generating linetiming signals defining printing on basic raster lines, and additionalline timing signals each defining printing on an additional raster line;and resolution conversion means adapted to receive repeatedly twice bitdata on the same line of the video signal corresponding to the linetiming signal and the additional line timing signal, respectively, saidresolution conversion means providing such a control that bit datacorresponding to a resolution of the LED head is extracted from eitherone of the bit data to be repeatedly received to generate a first signalrepresentative of a data sequence, and then the first signal istransmitted to the LED head in the form of a real printing data signalto be printed on the basic raster line in synchronism with the linetiming signal, and bit data not corresponding to the resolution of theLED head is extracted from another of the bit data to be repeatedlyreceived to generate a second signal representative of another datasequence, and then the second signal is transmitted to the LED head inthe form of a real printing data signal to be printed on the additionalraster line in synchronism with the additional line timing signal,wherein said control means further includes means for setting a firstLED head drive energy with which the basic raster lines are printed anda second LED head drive energy with which the additional raster linesare printed independently of each other.

In accordance with a still further preferred embodiment of the presentinvention, there is disclosed a non-impact printer provided with an LEDhead for printing and control means for providing a sequence control forthe printer in its entirety in response to a control signal and a videosignal from another controller, said LED head including: a shiftregister comprising a plurality of line buffers adapted for storing adata sequence corresponding to a resolution of the LED head, which isextracted from bit data of a printing data signal transmitted from thecontrol unit; and resolution conversion means for converting theremaining bit data not corresponding to the resolution of the LED headinto at least one other data sequence corresponding to the resolution ofthe LED head, and for providing such a control that the at least oneother data sequence is also stored in said line buffers, and the datasequence and the at least one other data sequence are alternately readout from said line buffers, so as to print the data sequencecorresponding to the resolution of the LED head on a basic raster lineand print the at least one other data sequence on at least oneadditional raster line, wherein said control means includes means forsetting a first LED head drive energy with which the basic raster linesare printed and a second LED head drive energy with which the additionalraster lines are printed independently of each other.

In accordance with a still further preferred embodiment of the presentinvention, there is disclosed a non-impact printer provided with an LEDhead for printing and control means for providing a sequence control forthe printer in its entirety in response to a control signal and a videosignal from another controller, said LED head including: a buffer forstoring a printing data signal on the preceding line transmitted fromthe control unit; a logical operation circuit for performing a logicaloperation of the printing data signal on the preceding line stored insaid buffer and the printing data signal now transmitted to generate areal printing data signal for printing on additional raster lines;storage means for storing the real printing data signal from saidlogical operation circuit and another real printing data signal forprinting on basic raster lines; and means for taking out alternately thereal printing data signal and the other real printing data signal fromsaid storage means, wherein said control means includes means forsetting a first LED head drive energy with which the basic raster linesare printed and a second LED head drive energy with which the additionalraster lines are printed independently of each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from a consideration of the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic block diagram of a control circuit of a non-impactprinter according to a preferred embodiment of the present invention;

FIG. 2 is a schematic block diagram showing a printer unit controlcircuit of a conventional non-impact printer;

FIG. 3 is a time chart useful for explanation of the conventionalnon-impact printer;

FIG. 4 is a schematic block diagram showing an LED head in theconventional non-impact printer;

FIGS. 5A, 5B and 5C, and 6A, 6B and 6C are views useful for explanationof printing states according to the conventional non-impact printer;

FIG. 7 is a schematic block diagram showing a print data receivingcircuit of a non-impact printer according to a first embodiment of thepresent invention;

FIG. 8 is a time chart useful for understanding how the print datareceiving circuit operates;

FIG. 9 is a detailed time chart useful for explanation of the print datareceiving circuit;

FIG. 10 shows bit data according to the received video signal;

FIG. 11 shows bit data according to the real print data signal;

FIGS. 12A, 12B and 12C, and 13A, 13B and 13C are views useful forexplanation of printing states according to the non-impact printer ofthe present invention;

FIGS. 14 and 15 are views illustrating LED light emission energyintensity and printing dots on a raster line according to a first and asecond scheme, respectively;

FIG. 16 is a schematic block diagram showing a print data receivingcircuit of a non-impact printer according to a second embodiment of thepresent invention;

FIG. 17A is a time chart useful for understanding how the print datareceiving circuit operates;

FIG. 17B is a detailed time chart useful for explanation of the printdata receiving circuit;

FIGS. 18A and 18B are views useful for explanation of a resolutionconversion in the non-impact printer according to the second embodimentof the present invention;

FIGS. 19A and 19B schematically show bit data before and after theresolution conversion, respectively, in the non-impact printer accordingto the second embodiment of the present invention.

FIG. 20 is a schematic block diagram showing a print data receivingcircuit of a non-impact printer according to a third embodiment of thepresent invention;

FIG. 21 is a time chart useful for understanding how the non-impactprinter according to the third embodiment of the present inventionworks;

FIG. 22 is a schematic block diagram of a control circuit of anon-impact printer according to another preferred embodiment of thepresent invention;

FIG. 23 is a schematic block diagram showing an LED head in thenon-impact printer according to the embodiment shown in FIG. 22;

FIG. 24 is a circuit diagram by way of example partially showing an LEDhead in the non-impact printer according to the embodiment shown in FIG.22;

FIG. 25 is a time chart useful for understanding how the non-impactprinter according to the embodiment shown in FIG. 22 operates;

FIG. 26 is a further partial circuit diagram by way of example showingan LED head in the non-impact printer according to the embodiment shownin FIG. 22;

FIG. 27 is a further time chart useful for understanding how thenon-impact printer according to the embodiment shown in FIG. 22operates; and

FIG. 28 is a block diagram showing exemplarily a drive energy settingcircuit S in FIGS. 1 and 22.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of a printer in accordance with the inventionwill be described in detail with reference to the drawings. FIG. 1 showsa block diagram of a control circuit in a non-impact printer accordingto an embodiment of the present invention, and FIG. 7 shows a blockdiagram of a print data receiving circuit.

In FIG. 1, a printing control unit or main control 1 comprises amicroprocessor, a ROM, a RAM, input/output ports, a timer and similarcomponents, and is provided inside a printing unit of a printer. Theprinting control unit 1 provides sequence control for the printer in itsentirety in response to control signals 10 and a video signal 11 fromanother controller, such as an interface control unit, a hostcontroller, or the like. Upon receipt of a print instruction included inthe control signals 10, the printing control unit 1 first causes a fusertemperature sensor 29 to sense whether or not a fuser 22 including aheater 22 a is in an acceptable temperature range, and if not, turns onthe heater 22 a in synchronism with a signal 21 to heat the fuser 22 toan acceptable temperature. Next, a motor (PM) 3 for adevelopment/transfer process is driven through a driver 2, andsimultaneously a high voltage power source 25 for charging is turned onin response to a charge trigger signal 23 to perform charging of adeveloping unit 27.

The sheets that are to be used are determined on the basis of a sheetremaining amount sensor 8 and a-sheet size sensor 9. A motor (PM) 5 forsheet feed is able to rotate in either direction through a driver 4. Themotor 5 first rotates in a reverse direction to move a sheet by apredetermined amount until a sheet sensor 6 senses the sheet, andsubsequently, it rotates in its regular direction to transfer the sheetto a printing device inside the printer.

Now an embodiment of a non-impact printer of the invention will bedescribed further taking by way of example a case in which printing isperformed with a resolution (the arrangement pitch in a raster directionof light emitting diode (LED) devices) of 300 dots per inch (DPI) by anLED head 19 in a printing unit of the non-impact printer, in which thevideo signal 11 that is received has a resolution of 600 DPI, and inwhich the resolution of the real printing image is 300 DPI in the rasterdirection and 1200 DPI (pseudo 600 DPI) in a printing direction (thesheet feed direction).

The printing control unit 1 transmits, at the time the sheet arrives ata printing ready point, a timing signal 12, including a line timingsignal 12 a and a raster timing signal, to another controller 1′, andreceives a video signal 11. The received video signal 11, which has beenedited in units of pages in the other controller or the host controllerand which has a resolution of 600 DPI (row and column), is supplied to aprint data receiving circuit R included in the printing control unit 1.The print data receiving circuit R is adapted to receive the videosignal 11 from the other controller and transmit the timing signal 12 tothe other controller.

FIG. 7 shows a block diagram of a first embodiment at such a print datareceiving circuit R. Referring to FIGS. 7, 8, 9, 10 and 11, the receivedvideo signal 11 is partially converted by a flip-flop 51 for resolutionconversion into a first signal A consisting of a data sequencecorresponding to the resolution of the LED head 19, and the resultantsignal from the conversion is transmitted through a selector 57 to theLED head 19 in the form of a real printing data signal 18 (300 DPI) soas to be printed on basic raster lines 102. Simultaneously, theremaining data of the received video signal 11, which is not convertedinto the first signal A, is converted by flip-flops 52 and 53 and an ORgate 54 into a second signal B consisting of another data sequence. Theresultant signal from the latter conversion is transmitted through aselector 56 to a line buffer 55 and then stored therein so as to beprinted on additional raster lines 120 each located at a distance{fraction (1/1200)} inch from the basic raster line 102 in a printdirection, or at an intermediate point of a print position for each 600DPI of the received video signal. A clock signal 18 a to be supplied tothe LED head 19 is divided in frequency by a flip-flop 58 to reduce itto one half for a video signal transfer clock signal 12 b which issupplied from the print control unit to the host controller.

A frequency multiplier 61 serves to provide an output which is two timesas high as the frequency of a line timing signal 12 a generated by aline timing signal generator 60, and generates an additional line timingsignal 12 c for printing on an additional raster line 120 during aninterval of a receiving timing of the line timing signals 12 a.

A clock signal generator 59 generates a clock signal which is suppliedto the flip-flop 58. The clock signal 18 a, which is delivered from anoutput terminal of the flip-flop 58, is supplied to the flip-flops 52and 53 as well as the LED head 19. A clock signal 18 b, which isdelivered from a reversal output terminal of the flip-flop 58, issupplied to an input terminal thereof and in addition to the flip-flop51.

Consequently, the flip-flops 51 and 52 are different from each other inthe timing of the clock signals 18 a and 18 b, so that they producedifferent data sequences. In other words, the flip-flop 51 outputs thefirst signal A as mentioned above, and the flip-flop 52 outputs a signalC comprising a data sequences which is obtained when the first signal Ais removed from the data sequence of the video signal 11. The signal Cis transmitted to the flip-flop 53, so that it outputs a signal D. Thesignals C and D are further transmitted to the logical OR gate 54, whichoutputs the second signal B.

The video signal 11 received with the resolution of 600 DPI, as shown inFIG. 10, is divided into two groups, as shown in FIG. 11, one includingdata which are printed with 300 DPI resolution as they are, and anotherincluding pseudo 600 DPI data each divided into two dots as shown byarrows. Those groups are printed separately on a different timing basis.Each of the dots represented by circles shown with broken lines on thebasic raster lines 102 in FIG. 11, which corresponds to the signal Coutputted from the flip-flop 52, is represented by two dots on theadditional raster lines 120 in FIG. 11, which correspond to the signal Boutput from the OR gate 54.

The printing control unit 1 transmits a line of real printing datasignal 18 and then a latch signal 17 to the LED head 19, so that thethinned out real printing data signal 18 (300 DPI) is held in the LEDhead 19. The LED head 19 includes a number of LED devices which arearranged in a raster direction. Upon receipt of a printing drive signal13, the LED head 19 is driven with an LED head drive energy E1 inaccordance with the held real printing data signal 18, so that anelectrostatic latent image is formed on a photoconductive drum 19′.

Next, when the sheet advances by {fraction (1/1200)} inch in a sheetfeed direction, and the printing control unit 1 switches the selectors56 and 57 to take out the data (pseudo 600 DPI) stored in the linebuffer 55 as a signal E. The signal E is transferred to the LED head 19in the form of the real printing data signal 18 in synchronism with theclock signal 18 a. At that time, no line timing signal 12 a is emittedto the host controller, and thus the above-mentioned operation iscarried out only in the printing control unit 1.

Then, the printing control unit 1 transmits a latch signal 17 to the LEDhead 19, so that the real printing data signal 18 (pseudo 600 DPI) isheld in the LED head 19. Upon receipt of a printing drive signal 13, theLED head 19 is driven with an LED head drive energy E2 in accordancewith the held real printing data signal 18, so that an electrostaticlatent image is formed on the photoconductive drum.

The LED head drive energies E1 and E2 are predetermined independently ofeach other, as shown in FIGS. 12 and 13, so as to obtain an equivalenceof the dot images formed when printing with the pseudo 600 DPIresolution and the dot images formed when printing with the basic 300DPI resolution.

According to the present embodiment, the conversion is performed in sucha manner that data is increased at a place located at a distance of{fraction (1/1200)} inch from a basic raster line. The LED head driveenergies E1 and E2 are predetermined so as to satisfy the relation.E1>E2, and while they can be varied depending on the developing unit 27,lenses, the characteristics of the toner, etc., they are represented by

E1=(0.4 to 0.6)×E

E2=(0.15 to 0.25)×E,

where E denotes the LED head drive energy at the standard 300 DPIresolution.

The printing control unit 1 includes a drive energy setting circuit Sfor predetermining the LED head drive energy E1 and E2 independently ofeach other. A block diagram of such a drive energy setting circuit isshown by way of example in FIG. 28.

In FIG. 28, prior to the printing operation, digital values, whichcorrespond to the LED head drive energies E1 and E2, respectively, aretransmitted from a CPU or the like in the printing control unit 1through a CPU bus to a latch A 201 and a latch B 202, respectively, andthen stored therein. At the time of printing, those latched data arealternately selected by a selector 204 in accordance with an output of atoggle flip-flop 203 which is operative in response to the additionalline timing signal 12 c, so as to load a decrement counter 205 inresponse to the additional line timing signal 12 c. The decrementcounter 205 generates a pulse output during a counting period of time.This pulse output may be used as the printing drive signal 13.

Referring FIGS. 14 and 15, there will be described some schemes forperforming printing with a resolution exceeding that of the LED head 19.In FIG. 14, light emission intensity 140 at the light emission point ofthe respective LED devices of the LED head 19 sufficiently exceeds thesensitivity threshold of the photoconductor drum (which will hereafterusually be shortened to the sensitivity of the drum), so that print dotsare formed at the associated light emission point positions. At thattime, the light emission intensity in intermediate portions M will beincreased owing to overlapping of light emission at the adjacent lightemission points to exceed the sensitivity of the photoconductor drumwhich is necessary to form an electrostatic latent image thereon, sothat the printing is performed at the associated intermediate portionsM. Thus, the adjacent dots are coupled by the exposure at theintermediate portions M. This scheme will be useful for printing on thebasic raster lines.

In FIG. 15, light emission intensity 140 at the light emission point ofthe respective LED devices of the LED head 19 is less than thesensitivity of the photoconductor drum which is necessary to form anelectrostatic latent image thereon, so that no print dots are formed. Onthe other hand, if it happens that simultaneous light emission occurs atthe adjacent light emission points, the synthesized light emissionintensity 141 exceeds the sensitivity of the photoconductor drum at theintermediate portions M. Consequently, it is possible to form dots atthe intermediate portions M, that is, it is possible to perform printingwith a resolution which is twice as high as that of the printer unit.This scheme will be useful for printing on the additional raster lines.

FIG. 16 shows a block diagram of a print data receiving circuit R, as analternative or second embodiment, shown in FIG. 1. In this embodiment,the real printing data for printing on the additional raster lines isobtained by means of a logical operation. Referring to FIGS. 16, and 17Aand 17B, the print data receiving circuit R shown in FIG. 16 includes aflip-flop 58 for dividing in frequency a clock signal f_(o) generated bya clock signal generator 59 to reduce it to one half, a line timingsignal generator 60, and a frequency multiplier 61 adapted to provide anoutput which is two times as high as the frequency of a line timingsignal 12 a generated by the line timing signal generator 60 and togenerate an additional line timing signal 12 c for printing on anadditional raster line 120 during the respective timing intervals of theline timing signal 12 a.

The clock signal f_(o), which is generated by the clock signal generator59, is supplied to the flip-flop 58, and in addition to the flip-flops83 to 88. A clock signal 18 a, which is delivered from an outputterminal of the flip-flop 58, is supplied to the LED head 19 in FIG. 1.On the other hand, a clock signal f₁, which is delivered from a reversaloutput terminal of the flip-flop 58, is supplied to an input terminalthereof and in addition to a flip-flop 96 and a delay circuit 94.

The print data receiving circuit R shown in FIG. 16 further comprises aselector 81, a line buffer 82 connected to the selector 81 for storing5120 bits of video signal 11, flip-flops 83, 84 and 85 for latching 3bits of bit data in data signal S, taken out from the line buffer 82,flip-flops 86, 87 and 88 for latching three bits of bit data in thevideo signal 11, an AND gate 89 for taking a logical AND of therespective outputs of the flip-flops 84 and 88, a further AND gate 90for taking a logical AND of the respective outputs of the flip-flops 84and 86, an OR gate 92 for taking a logical OR of the respective outputsof the flip-flop 83, the flip-flop 85, the AND gate 89 and the AND gate90, a flip-flop 93 for taking out the output of the OR gate 92, a delaycircuit 94 for providing a delay of an operational timing of theflip-flop 93 to an operational timing of the flip-flop 96, and aselector 95.

The video signal 11, which has been edited in units of pages in theother controller or the host controller and which has 600 DPIresolution, is supplied through the selector 81 to the line buffer 82 soas to be stored therein in the form of 5120 bits of bit data with theresolution of 600 DPI, when the selector 81 is operated to provide adirection of data transfer in which the line buffer 82 receives thevideo signal in accordance with an input/output selection signal f_(x)for the selector 81 which is generated from the clock signal generator.In addition, the video signal 11 is latched in the flip-flops 86, 87 and88 in the form of 3 adjacent bits of bit data. Likewise, the videosignal 11 for the preceding line, which has been stored in the linebuffer 82, is latched in the flip-flop 97 at a timing determined by aclock signal f_(o) generated by a gate 98, when the selector 81 isoperated to provide a direction of data transfer in which the linebuffer 82 outputs the video signal in accordance with the input/outputselection signal f_(x). In addition, the video signal 11 is latched inthe flip-flops 83, 84 and 85 in the form of 3 adjacent bits of bit data.A logical operation is performed on these data by the gates 89, 90 and92 as represented by the following logical expression: $\begin{matrix}\begin{bmatrix}B_{N,{2j}} & = & {\left( A_{N,{{2j} - 1}} \right) + \left( A_{N,{{2j} + 1}} \right) +} \\\quad & \quad & {{\left( A_{N,{2j}} \right) \cdot \left( A_{{N + 1},{{2j} - 1}} \right)} +} \\\quad & \quad & {{\left( A_{N,{2j}} \right) \cdot \left( A_{{N + 1},{{2j} + 1}} \right)},}\end{bmatrix} & (1)\end{matrix}$

where A_(m,n) represents bit data on the m-th and n-th lines of thereceived 600 DPI video signal. If n is an even number, then itrepresents an LED head resolution position. If n is an odd number, thenit does an intermediate position of LED head resolution positions. Inaddition, B_(m,n) represents bit data on an additional raster data line.

Thus, the bit data, which is subjected to the logical operation based onthe current video signal 11 that has been entered and the previous videosignal 11 on the preceding line, is supplied to the flip-flop 93 so thatthe resolution in the raster direction is converted into that in thesheet transfer direction as the intermediate point data. The resultantbit data from the conversion is transmitted as the real printing data 18through the selector to the LED head 19 in FIG. 1.

FIG. 18A shows the states of a resolution conversion of the bit data,and FIG. 18B shows the coordinates of the raster lines. When the logicaloperation is carried out in accordance with equation (1) as set forthabove, the bit data that are represented by circles shown with dottedlines on the basic raster lines 102 in FIG. 18A are converted into thebit data represented by circles shown with solid lines on the additionalraster lines 120.

More in detail, if it is considered that a dot “b” represented by acircle in FIG. 18A is applied to the equation (1) set forth above, dataof a dot “a” exists at the second term of the right member of theequation (1), and thus the dot “b” is generated as printing data.Similarly, regarding a dot “c”, data of the dot “a” exists at the firstterm of the right member of the equation (1), and thus the dot “c” isgenerated as printing data. Regarding a dot “d”, data of dots “e” and“f” exist at the fourth term of the right member of the equation (1),and thus a dot “d” is generated as printing data. Regarding a dot “g”,data of dots “h” and “i” exist at the third term of the right member ofthe equation (1), and thus a dot “g” is generated as printing data.

FIG. 18B shows the coordinate of the related raster lines before andafter the noted coordinate B_(N, 2 j) on an additional raster line, onwhich it is determined whether or not a real printing data is to beproduced.

FIG. 19A schematically shows bit data before the resolution conversion,and FIG. 19B schematically shows the data after the resolutionconversion. The video signal 11 received with a resolution of 600 DPI,as shown in FIG. 19A, is divided into two groups, as shown in FIG. 19B,one including bit data which are printed on the basic raster lines with300 DPI resolution as they are, and another including bit data which areto be subjected to a logical operation according to equation (1) setforth above and to be printed on the additional raster lines.

The clock signal 18 a that is supplied to the LED head 19 is generatedby flip-flop 58, which divides the clock signal F_(o) in frequency asshown in FIG. 16. More specifically, the frequency of the clock signal18 a is half that of the clock signal f_(o) generated by the clocksignal generator 59. The real printing data signal 18 transferred to theLED head 19 is latched after completion of a line of data. Upon receiptof a printing drive signal 13, the LED head 19 is driven with an LEDhead drive energy E2 in accordance with the held real printing datasignal 18, so that an electrostatic latent image is formed on aphoto-conductive drum.

Next, when the sheet advances by {fraction (1/1200)} inch in the sheetfeed direction, the printing control unit 1 switches the selector 81 toread out the video signal 11 (600 DPI data) stored in the line buffer82. The read out data is applied to the flip-flop 96 so that theresolution in the raster direction is converted into that in the sheettransfer direction. The resultant data from the resolution conversion,that is, an output signal of the flip-flop 96, is transferred throughthe selector 95 to the LED head 19 in the form of the real printing datasignal 18 in synchronism with the clock signal 18 a. At that time, thereis generated no line timing signal 12 a to the host controller, and thusthe above-mentioned operation is carried out only in the printingcontrol unit 1. Then, the printing control unit 1 transmits a latchsignal 17 to the LED head 19, so that the real printing data signal 18,which has been subjected to resolution conversion, is latched or held inthe LED head 19. Upon receipt of the printing drive signal 13, the LEDhead 19 is driven with an LED head drive energy E1 in accordance withthe held real printing data signal 18, so that an electrostatic latentimage is formed on the photoconductive drum.

The LED head drive energies E1 and E2 are predetermined, as shown inFIGS. 12 and 13, so as to obtain an equivalence of the dot images formedwhen printing with the pseudo 600 DPI resolution and the dot imagesformed when printing with the basic 300 DPI resolution.

According to the instant embodiment, similar to the first embodiment,the conversion is performed in such a manner that data is increased at aplace that is spaced apart by a distance of {fraction (1/1200)} inchfrom a basic raster line. The LED head drive energies E1 and E2 arepredetermined so as to satisfy the relation, E1>E2, and while they canbe varied depending on the developing unit 27, lenses, thecharacteristics of the toner, etc., they are represented by

E1=(0.4 to 0.6)×E

E2=(0.15 to 0.25)×E,

where E denotes the LED head drive energy at the standard printingdensity of 300 DPI.

FIG. 20 is a block diagram schematically showing another alternativeembodiment the print data receiving circuit R shown in FIG. 1. The printdata receiving circuit R shown in FIG. 20 comprises a clock signalgenerator 59, a line timing signal generator 60, a resolution conversioncircuit 100, flip-flop 97, a print drive signal generator circuit 98 anda latch signal generator circuit 99.

Referring to FIGS. 20 and 21, the printing control unit 1, whichincludes the print data receiving circuit R mentioned above, transmits atiming signal 12, including a line timing signal 12 a and a rastertiming signal, to the another controller. Upon receipt of the timingsignal 12, the another controller transmits to the printing control unit1 original image data which have been edited in units of pages and whichare stored in its memory, in the form of a video signal 11 having acolumn resolution of 1,200 DPI and a row resolution of 600 DPI, which isrepeated two times for the same raster line. The received video signal11 is supplied to the print data receiving circuit R.

Such a video signal 11 has a resolution that exceeds the resolution ofLED head 19, as in previous embodiments. A set of bit data provided bythe video signal 11 is converted by the resolution conversion circuit100 into real printing data 18 with 300 DPI resolution in the rasterdirection. More particularly, the video signal 11 on a first linecorresponding to a raster line is converted into a first signalcomprising only even numbered bit data, with odd numbered bit data inthe raster direction being removed, and then the first signal istransmitted to the LED head 19 in the form of the real printing datasignal 18 together with the clock signal 18 a. Since the video signal 11has a row resolution of 600 DPI, it will be apparent that the evennumbered bit data provide a real printing data signal 18 having aresolution of 300 DPI, the same as the resolution of LED head 19. Ashift register (e.g. 19 a in FIG. 4) in the LED head 19 sequentiallystores the real printing data signal 18 in synchronism with the clocksignal 18 a. The printing control unit 1 transmits a line of realprinting data signal 18 and then a latch signal 17 to the LED head 19prior to receiving the subsequent data from the host controller, so thatthe thinned out real printing data signal 18 is held in the LED head 19.A latch (e.g. 19 b in FIG. 4) in the LED head 19 holds a line of realprinting data signal 18 stored in the shift register 19 a in accordancewith the latch signal 17. Upon receipt of a printing drive signal 13from the printing control unit 1, the LED head 19 is driven with an LEDhead drive energy E1 so as to illuminate the LED devices according tothe held real printing data signal 18. Optional information from the LEDhead 19 is received by a photoconductor drum, parts of which arecorrespondingly charged with a negative potential in the form of anelectrostatic latent image with dots elevated in potential.

Next, when the sheet advances by {fraction (1/1200)} inch in the sheetfeed direction, the printing control unit 1 again transmits the timingsignal 12 to the host controller and receives the video signal 11 on asecond line corresponding of the same raster line. That is, the same setof bit data is transmitted, as will be apparent from the depiction ofvideo signal 11 in FIG. 21. The video signal 11 is converted into asecond signal by the resolution conversion circuit 100 in such a mannerthat even numbered bit data in the raster direction are thinned out orremoved, and the remained odd numbered bit data are subjected to alogical operation to take a logical OR on the respective odd numberedbit data and the associated odd numbered bit data located immediatelybefore. The printing control unit 1 transmits a line of real printingdata signal 18 and then a latch signal 17 to the LED head 19 prior toreceiving the subsequent video signal 11 from the host controller, sothat the thinned out real printing data signal 18 is held in the LEDhead 19. Upon receipt of a printing drive signal 13 from the printingcontrol unit 1, the LED head 19 is driven with an LED head drive energyE2 in accordance with the held real printing data signal 18, so that anelectrostatic latent image is formed on the photoconductive drum.

Next, another embodiment of a non-impact printer according to thepresent invention will be described referring to FIGS. 22-25. FIG. 22shows a control circuit of the non-impact printer according to thisembodiment, FIG. 23 is a block diagram showing an LED head 30 in thenon-impact printer, FIG. 24 is a partial circuit diagram exemplarilyshowing the LED head 30 in the non-impact printer, and FIG. 25 is a timechart useful for understanding the non-impact printer according to theembodiment.

In FIG. 22, reference numbers that are the same as those in FIG. 1denote like elements. A control circuit of the non-impact printer inFIG. 22 includes an LED head 30 adapted to receive a printing datasignal 20 of 600 DPI from a printing control unit 301. Morespecifically, at this stage, the printing data signal 20 is providedwith the same resolution as the video signal 11. The printing controlunit 301 is adapted to generate a reset signal 21 a to reset flip-flopscontained in the LED head 30.

The LED head 30 shown in FIG. 23 comprises a shift register 30 aconsisting of raster line buffers 1 through n, a latch 30 b, an LEDgroup 30 c including LED devices corresponding to the raster lines ofdots, a driver group 30 d consisting of drivers for the LED devices ofthe LED group 30 c, and a resolution conversion circuit 30 e forconverting the resolution of the printing data signal 20.

Now, the present embodiment of the non-impact printer of the inventionwill be described taking by way of example a case in which printing isperformed whereby the resolution of the received video signal 11 is 600DPI, and the resolution of the real printing image is 300 DPI in theraster direction and 1200 DPI in the printing direction. It is notedthat the relation of the video signal 11 before and after conversion ofthe resolution and a real printing data signal 20 a is the same as inthe first embodiment. Thus, the present embodiment will be explainedalso referring to FIGS. 10-13 on a common basis.

Referring to FIG. 10 again, even numbered bit data in the rasterdirection of the received 600 DPI image data correspond to locations(300 DPI) of the LED devices of the LED head 30. They are printed on araster line as they are. On the other hand, odd numbered bit data in theraster direction of the received image data do not correspond tolocations of the LED devices of the LED head 30. Thus, they are not ableto be printed on the same raster line. Instead, each of the odd numberedbit data is divided into portions located right and left at a distanceof {fraction (1/300)} inch from each other, and is printed on anadditional raster line located at a short distance, for instance{fraction (1/1200)} inch, from the basic raster line in the sheettransfer direction.

A drive energy E1 on the basic raster line and a drive energy E2 on theadditional raster line is predetermined, as shown in FIGS. 12 and 13, soas to obtain an equivalence of a real printing image formed with thepseudo 600 DPI resolution and a real printing image formed with thebasic 300 DPI resolution.

Accordingly, the drive energies E1 and E2 are predetermined so as tosatisfy the relation, E1>E2, and they are represented by

E1=(0.4 to 0.6)×E

E2=(0.15 to 0.25)×E,

where E denotes the drive energy at the standard density, 300 DPI.

Again referring to FIG. 22, upon receipt of a control signal 10 for aprint instruction from a host controller, the printing control unit 301serves to feed a print sheet to a print ready position. The printingcontrol unit 301 transmits, when the sheet arrives at the printing readyposition, a timing signal 12, to the other controller, not shown, andreceives a video signal 11. The received video signal 11, which has beenedited in units of pages in the other controller or host controller andwhich has 600 DPI resolution, is transmitted together with a clocksignal 18 a through the printing control unit 301 to the LED head 30 inthe form of a printing data signal 20.

Next, operation of the LED head 30 will be described referring to FIGS.23, 24 and 25. FIG. 24 shows partially, and more specifically, the LEDhead 30 shown in FIG. 23. The printing data signal 20 is sequentiallysupplied to flip-flops 41 and 42. Real printing data 20 a is outputtedfrom a logical OR gate 44, and then supplied together with the clocksignal 18 a to the shift register 30 a. The shift register 30 a includes5120 flip-flops which are arranged in series. Those flip-flopsconstitute two line buffers. In other words, each of the line bufferscomprises 2,560 flip-flops. As shown in the figure, the output signalsof every other flip-flop are applied to the latch 30 b. The clock signal18 a is applied to the respective flip-flops. A flip-flop 45 is adaptedto produce alternately binary values of “1” and “0”. The flip-flops 41,42, and 45, a logical AND gate 43 and the OR gate 44 constitute incombination the resolution conversion circuit 30 e.

In the resolution conversion circuit 30 e, the OR gate 44 receives theprinting data signal 20 and an output of the AND gate 43. The AND gate43 receives an output signal f of the flip-flop 42 and an output signalg of the flip-flop 45. The output signal g of the flip-flop 45 iscontrolled in such a manner that when odd numbered bit data of theprinting data signal 20 of 600 DPI resolution are transmitted, it isgiven with a binary value of “1”, and when even numbered bit data aretransmitted, it is given with a binary value of “0”. The output signal fof the flip-flop 42 holds bit data which is delayed by two bits by theflip-flops 41 and 42. Consequently, the AND gate 43 outputs alternatelythe odd numbered bit data immediately before the current odd numberedbit data and the binary value “0”.

Thus, the shift register 30 a receives alternately data which isobtained by taking a logical OR of the odd numbered bit data of the 600DPI printing data signal 20 and the odd numbered bit data immediatelybefore the current odd numbered bit data, and the even numbered bitdata. That is, the shift register 30 a receives alternately the bit datato be printed on the basic raster lines and the bit data to be printedon the additional raster lines.

The printing control unit 301 transmits a latch signal 17 to the LEDhead 30, so that the latch 30 b stores data of 300 DPI resolution whichis transferred to the raster line buffer provided in the shift register30 a corresponding to the even numbered bit data. Upon receipt of aprinting drive signal 13 from the printing control unit 301, the LEDhead 30 is driven with a drive energy E1 so as to form an electrostaticlatent image on the photoconductor drum.

Next, the sheet advances by {fraction (1/1200)} inch in the sheet feeddirection, and the printing control unit 301 transmits one clock pulseof the clock signal 18 a and then the latch signal 17 to the LED head30. As a result, data stored in the raster line buffer associated withthe odd numbered bit data in the shift register 30 a are shifted to theraster line buffer associated with the even numbered bit data in theshift register 30 a and then latched or held in the latch 30 b. Uponreceipt of a printing drive signal 13 from the printing control unit301, the LED head 30 is driven with a drive energy E2 so as to form anelectrostatic latent image on the photoconductor drum.

Next, a further embodiment of a non-impact printer according to thepresent invention will be explained referring to the drawings, includingFIG. 22, FIG. 26, which is a partial circuit diagram by way of exampleshowing a modified LED head 30 for use in the arrangement shown in FIG.22, and FIG. 27, which is a time chart useful for explanation of thenon-impact printer according to the further embodiment.

This embodiment is intended to obtain the real printing data forprinting on the additional raster lines by means of a logical operation.Referring to FIG. 26, the LED head 30 comprises a shift register 30 a, alatch 30 b, an LED group 30 c including LED devices corresponding to theraster lines of dots, a driver group 30 d of drivers for driving the LEDdevices of the LED group 30 c, and a buffer 30 f for storing therein theprinting data signal 20 on the preceding line corresponding to 5,120dots.

Each of the shift register 30 a and the buffer 30 f includes 5,120flip-flops which are arranged in series. The shift register 30 acomprises a first group 32 a of flip-flops and a second group 32 offlip-flops, each group having 2,560 flip-flops. As shown in the figure,the output signals of every other flip-flop are applied to the latch 30b.

The LED head 30 shown in FIG. 26 further includes a logical operationcircuit for performing a logical operation on the printing data signal20 on the preceding line stored in the buffer 30 f and the printing datasignal 20 now transmitted. The logical operation circuit comprisesflip-flops 65 and 66 for latching two dots of bit data in the printingdata signal 20 on the preceding line transferred from the buffer 30 f,flip-flops 66 and 68 for latching two dots of bit data in the printingdata signal 20 on the current line or the now noted line, an AND gate 69for taking a logical AND of the output of the flip-flop 65 and theprinting data signal 20, a further AND gate 70 for taking a logical ANDof the respective outputs of the flip-flops 65 and 68, an OR gate 71 fortaking a logical OR of the printing data signal 20, the output signal ofthe flip-flop 66, an output signal of the AND gate 69 and the outputsignal of the AND gate 70, a flip-flop 72 adapted to producealternatively binary values of “1” and “0”, an AND gate 73 for impartinga logical AND on the output signal of the OR gate 71 and the outputsignal of the flip-flop 72, and an OR gate 74 for imparting a logical ORon an output signal of the AND gate 73 and the printing data signal 20.

In the LED head 30 mentioned above, a real printing data signal 20 b andthe clock signal 18 a are supplied to the shift register 30 a. In suchan LED head, the printing data signal 20 on the preceding line stored inthe buffer 30 f and the printing data signal 20 that is now transmittedare logically combined by the above-mentioned logical operationcircuitry in accordance with the logical expression (1) set forth above,so that real printing data for printing on the additional raster linescan be obtained.

More specifically, as a result of the above-mentioned logical operation,the odd numbered bit data are provided and the flip-flop 72 serves totransmit to the shift register 30 a alternately the odd numbered bitdata and the even numbered bit data. As a result, the odd numbered bitdata are set to the first stage of flip-flop group 32 a and then latchedin the latch 30 b in accordance with the latch signal 17.

As shown in FIG. 27, after latching of the odd numbered bit data, theLED devices are supplied with a drive energy E2. Further, the printingcontrol unit 301 transmits one clock pulse of the clock signal 18 a andthen the latch signal 17 to the LED head 30, so that the even numberedbit data (for printing on the basic raster lines) are set to the firststage of flip-flop group 32 a and then latched in the latch 30 b inaccordance with the latch signal 17. Subsequently, when the sheetadvances by {fraction (1/1200)} inch in the sheet feed direction, theLED devices are provided with the drive energy E1. This operation isrepeatedly carried out on the respective lines so as to form anelectrostatic latent image on the photoconductor drum.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by thoseembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

What we claim is:
 1. A non-impact printer comprising: signal generatormeans for receiving a video signal, including first and second bit data,and generating a first printing data signal corresponding to the firstbit data of the video signal received to form a print line of printingdots; drive energy setting means for setting a drive energycorresponding to the first printing data signal generated; and a printerhead operative in response to the drive energy set for generating dotsof light in a print line at a first resolution to form on aphotoconductive body an electrostatic latent image of the video signal,the photoconductive body having a sensitivity threshold, above whichwith a dot of light having the drive energy a printing dot is formed onthe photoconductive body; said signal generator means being operative inresponse to the second bit data of the video signal, which are of asecond resolution of printing dots higher than the first resolution, toconvert the second bit data, which does not correspond to the printingdots of the print line at the first resolution, into a second printingdata signal forming printing dots adjacent to each other in the printline at the first resolution; said drive energy setting means beingoperative in response to the second printing data signal to set thedrive energy of a dot of light at such a level that the sensitivitythreshold is reached not by the drive energy of a dot of light in theprint line at the first resolution but is reached by the drive energysynthesized by the dots of light which are adjacent to each other andcorrespond to the second printing data signal in the print line.
 2. Anon-impact printer according to claim 1, wherein the printing dots areformed in a direction of the print line.
 3. A non-impact printeraccording to claim 1, further comprising storage means connected to saidsignal generator means for storing therein the first and second printingdata signals.
 4. A non-impact printer according to claim 3, wherein theprinting dots are formed in a direction of the print line.